Track covariance to be changed

[clementhelsens]

Delphes returns the full covariance:

https://github.com/delphes/delphes/blob/master/modules/TrackCovariance.cc#L122

but in edm4hep we use the diagonal terms also stored in delphes:

k4SimDelphes/converter/src/DelphesEDM4HepConverter.cc

Lines 445 to 449 in bf31367

	covMatrix[0] = cand->ErrorD0 * cand->ErrorD0;
	covMatrix[5] = cand->ErrorPhi * cand->ErrorPhi;
	covMatrix[9] = varOmega;
	covMatrix[12] = cand->ErrorDZ * cand->ErrorDZ;
	covMatrix[14] = cand->ErrorCtgTheta * cand->ErrorCtgTheta;

We need to change that to store the full covariance matrix including correlations. Need to pay attention to the units

[tmadlener]

Here we also have to pay attention that the full covariance is only available from more recent delphes versions.

[vvolkl]

Yes indeed, In fact only the latest 3.4.3pre06 tag can be used for this, the previous ones have unit bugs. @clementhelsens I think we can just port the fccsw code for this, that has been tested, right? https://github.com/HEP-FCC/FCCSW/blob/master/Sim/SimDelphesInterface/src/DelphesSaveChargedParticles.cpp

[clementhelsens]

@vvolkl , yes the FCC implementation has been tested. The only difference is that the track basis is different in FCCSW (ACTS like)

[andresailer]

Also note: key4hep/EDM4hep#108

[tmadlener]

Is this still open or has this been fixed (see #27) and can be closed? In any case related: #46

[clementhelsens]

yes, this can be closed